In the prior art, a MEMS (Microelectromechanical Systems) microphone is a microphone manufactured based on the MEMS technique. Generally, a MEMS microphone includes a MEMS microphone chip and an integrated circuit (ASIC), for converting received sound wave into sound electrical signal.
Typically, a MEMS microphone chip has a resonance frequency at its high frequency side. The resonance frequency can depend on the Helmholtz resonator formed by the front chamber (or back chamber/cavity), the resonance frequency of the diaphragm and so on.
Generally, the MEMS microphone chip has a narrow bandwidth of the resonance frequency. Furthermore, the resonance frequency is uncertainty due to manufacturing tolerance. Therefore, in the prior art, the MEMS microphone is not used to directly detect sound of a certain frequency.
In the prior art, a filter is provided in the ASIC to filter the sound electric signal. However, the SNR of the MEMS microphone chip will be degraded because it needs extra electronic components. In addition, these extra electronic components will cause extra product complexity. For example, on-chip capacitor and on-chip resistor will be needed.